[6.06] The Effects of Thermal Heating Via the Dissipation Of Turbulence on the WIM/DIG

A. Minter, D. S. Balser (NRAO)

The observed properties of the diffuse ionized gas (DIG) in our Galaxy
are not easily reconcilable with simple photoionization models.
Photoionization models, however, can reproduce the observed properties
of H \scriptstyle II regions. This suggests that there are different or
additional physical processes at work in the DIG.
The He \scriptstyle I \lambda 5876/H\alpha line ratio indicates
that a soft ionizing spectrum is needed in the DIG while
[N \scriptstyle II] \lambda 6583/H\alpha
and [S \scriptstyle II] \lambda 6716/H\alpha line ratios
indicate that a harder ionizing spectrum is needed if only
photoionization is to explain the properties of the DIG.
Minter and Spangler (1997, ApJ, in press) have shown that the thermal
heating due to the dissipation of the turbulence is likely to be an important
heating mechanism in the DIG while being unimportant in
H \scriptstyle II regions.

We have developed a
model of the DIG whereby it is ionized by a relatively soft ionizing
spectrum (T_eff \le 32,000\, K) and is also heated by an
additional thermal mechanism: the dissipation of turbulence. This
model predicts the same electron temperature,
[N \scriptstyle II] \lambda 6583 ratio,
[S \scriptstyle II] \lambda 6716
ratio and He \scriptstyle I \lambda 5876
ratio as observed in the DIG.
The model suggests that the observed
[O \scriptstyle III] \lambda 5007
emission from the diffuse
ISM does not originate from the oxygen in the DIG. Without the
turbulent thermal heating term, this model will not reproduce the
observed properties of the DIG. The dissipation of turbulence may
also be important in other phases of the ISM.

The author(s) of this abstract have provided an email address for comments about the abstract: tminter@nrao.edu